This invention relates to articles having an abradable surface portion and, more particularly, to turbomachinery high temperature superalloy articles having an abradable surface portion.
Gas turbine engine efficiency depends, at least in part, on reduction and preferably elimination of gas stream leakage between stationary and rotating members. For example, in the hot operating turbine portions of the engine, a gaseous stream of products of combustion are expanded through rotating turbine blades which cooperate with an opposed stationary shroud in a sealing relationship. Leakage around such a seal can reduce the effective extraction of energy from the gaseous stream. Abradable sealing means for such an application has included use on the shroud of various porous or fibrous metallic or non-metallic abradable materials. During operation, rotating turbine blade tips and the abradable sealing means generally approach one another into an interference relationship to avoid leadage outside of the gaseous stream.
As the operating temperatures and conditions in a gas turbine engine have become more strenuous, the known porous or fibrous abradable materials have experienced excessive oxidation or erosion or both.